This invention relates to a direct current interrupter for interrupting a large direct current, using a plurality of interrupter units.
Generally a direct current interrupter is used to interrupt direct current, whenever necessary, in an electric system. Thus, it effectively makes the system function more dynamically in transmitting direct current or in converting direct current into alternating current to be applied to a loading point. When direct current is relatively small, it is sufficient to use only one direct current interrupter of commutation type, wherein a commutation condenser is connected in parallel to, for example, an interrupting portion and vibrating current generated by the condenser is superposed on an input direct current thereby to form a non-current point. The interrupter of this type, however, cannot interrupt a large current.
To interrupt a large direct current, a plurality of parallel branch circuits have been conventionally used. More precisely, a large direct current is shunted to flow through the parallel branch circuits each having an interrupter unit with an interrupting capacity corresponding to the shunted direct current, and the interrupter units are operated substantially at the same time. FIG. 1 shows one of such large direct current interrupter connected to a pair of bus bars X and Y. The interrupter comprises an input terminal A and an output terminal B. Through the bus bars A and B a direct current to be interrupted flows. Between the input and output terminals are arranged four parallel branch circuits through a first common connecting portion A0 at the input side thereof and a second common connecting portion B0 at the output side thereof, and two-point interrupter units P1, P2, P3 and P4 are connected to the branch circuits R1, R2, R3 and R4, respectively. Arrows in FIG. 1 show the direction in which current flows. Each of interrupter units P1, P2, P3 and P4 is provided with two interrupting portions S1 and S2, S3 and S4, S5 and S6, and S7 and S8, respectively, and the interrupting portions S1 to S8 are arranged on a same plane and connected so as to cause current to flow in opposite direction in the adjacent interrupting portions.
In the known interrupter, however, the interrupter units are not arranged properly, causing the following troubles. At the interrupter unit of one of the branch circuit a magnetic field is generated by the other branch circuits. The magnetic field is intense enough to affect arcs generated at one or more interrupting portions. In addition, the branch circuits have different DC resistance and different reactances, and different currents therefore flow through them. As a result, the interrupter often become inoperative.